19 Nov
2008
19 Nov
'08
1:27 p.m.
Asiri Rathnayake wrote:
Hi Devs,
I'm working on implementing the style filtering functionality of
xwiki-office-importer application. But first, i need to make sure that I'm
clear about the policy and the correct approach towards filtering style
information from imported office documents. I would really appreciate your
input on this because I'm not an expert on either html or css :)
Ok, I plan to do two types of filtering. One is filtering various attributes
of various elements (like removing bgcolor attribute from the <body>
element). And the second one is filtering css related stuff. Let's take one
by one.
1. Filtering attributes.
This is quite straight-forward but i see two possible approaches.
* The first approach is to keep a list of attributes that we allow when
importing documents. We'll scan each and every tag and strip off any
unwanted attributes present.
* The second approach is to associate each tag with what attributes we allow
for that tag. A list of legal attributes for common tags is presented here
http://www.devx.com/projectcool/Article/19816. Similarly, we'll have our
tag_name->allowed_attributes mapping and filter all other attributes
present.
I'm currently leaning towards the second option, WDYT ?
Second sounds better from a functional perspective. However, we must be
sure we define this list in a clean way, and take care about
performance. We definitely don't want inline array definitions in the
java source files.
2. Filtering css styles.
Ok, there are three ways one can associate css with html content. Let's take
one by one.
(i) External Style Sheet
Well, AFAIK OpenOffice server does not produce this type of output when
converting office documents into html. I mean it doesn't output html files
that refer external css files. So I guess this is something we don't need to
worry about.
(ii) Internal Style Sheet
This is something we need to worry about. OpenOffice server produces html
pages with content like <head><style
type="text/css">....</style></head>.
Currently we strip off <style> tags completely regardless of the filtering
mode (i.e whether styles are set to be filtered or not <style> tags get
removed). Does this behaviour need to change ?
(iii) In-line Styles
This is the most common type of styling found (Example : <p
style="....">).
Present behaviour is to strip off this style attribute completely (if
filterStyles is set to true). The question is, there are some inline styles
that directly maps to xwiki 2.0 syntax like <p
style="font-weight:bold">,
what are we going to do about these ?
In any case, I will have to parse the in-line style attribute string to
filter those style directives that are not necessary. The complete grammar
for in-line style attributes seems to be a bit complicated to be hand
crafted (http://www.w3.org/TR/css-style-attr) although in OpenOffice
converted documents i have only seen the "key:value;key:value" format. What
should be the correct approach to parse the style attribute string ?
Thank you very much for your ideas. :)
All cases can be covered by using a CSS library. We already use css4j in
the export (pdf) implementation, and although it has several
limitations, this library is a good starting point. Vincent, could you
put the latest release (0.10) in our externals? There have been lots of
changes since 0.4, which would also help our PDF export.
--
Sergiu Dumitriu
http://purl.org/net/sergiu/